Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polyethelene terephthalate (PET) material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
As an illustration, injection molding of PET material involves heating the PET material (ex. PET pellets, PEN powder, PLA, etc.) to a homogeneous molten state and injecting, under pressure, the so-melted PET material into a molding cavity defined, at least in part, by a female cavity piece and a male core piece mounted respectively on a cavity plate and a core plate of the mold. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient enough to keep the cavity and the core pieces together against the pressure of the injected PET material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected PET material is then cooled to a temperature sufficient to enable ejection of the so-formed molded article from the mold. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core piece. Accordingly, by urging the core plate away from the cavity plate, the molded article can be demolded, i.e. ejected off of the core piece. Ejection structures are known to assist in removing the molded articles from the core halves. Examples of the ejection structures include stripper plates, ejector pins, etc.
One consideration for economical operation of the molding system is cycle time or, in other words, time that elapses between a point in time when the cavity and core halves are closed and the molded articles are formed and a subsequent point in time when they are opened and the molded articles are removed. As one will appreciate, the shorter the cycle time, the higher the number of molded articles that can be produced in a particular mold in a given time. One attempt to minimize the cycle time is a so-called “post-mold cooling” process. Generally speaking, the post-mold cooling process involves removing the molded articles from the mold once they are sufficiently cooled to enable ejection of the molded articles without causing significant deformation to the molded articles during its transfer to a post-mold cooling apparatus. Post mold cooling then occurs independently (but in parallel) to the injection cycle of the molding machine.
An example of the post-mold cooling apparatus is disclosed in a commonly owned U.S. Pat. No. 7,104,780 issued to Domodossola et al. on Sep. 12, 2006. More specifically, Domodossola et al. discloses a post-mold cooling apparatus for handling and cooling molded articles in an injection molding machine having a fixed platen, a movable platen, a core half, and a cavity half. The post-mold cooling apparatus includes a take-off device coupled to the fixed platen is configured to receive molded articles from either the core half or the cavity half. The post-mold cooling apparatus also includes a treatment device coupled to the movable platen that is configured to cool and extract the molded articles carried by the take-off device. In operation, the take-off device moves linearly inboard of the mold halves to position a first set of molded article carriers on the take-off device to receive hot molded articles from the mold's core half, once the hot molded articles have been received in the first set of molded article carriers the take-off device moves linearly outboard of the mold halves. The subsequent movement of the movable platen to close the mold in the next molding cycle causes a first set of treatment pins on the treatment device to engage the hot molded articles in the first set of molded article carriers of the take-off device, a second set of treatment pins on the treatment device to engage partially cooled molded articles previously received in a second set of molded article carriers on the take-off device, and a set of molded article pickers on the treatment device to engage cooled molded articles previously received on a third set of molded article carriers on the take-off device. When the movable platen opens again, the cooled molded articles are extracted from the third set of molded article carriers by the set of molded article pickers. When the movable platen is fully open, the treatment device is rotated to a drop position and the cooled molded articles are released from the molded article pickers and onto a conveyor or into some other post-mold device. When the molded articles have been released from the molded article pickers the treatment device is rotated back to a pick position and the cycle repeats.
With reference to FIG. 2, a typical molded article carrier 28 for use with the foregoing take-off device is shown. The molded article carrier 28 includes a cooling tube 30, an insert 32, a sleeve 34, and a fastener 36. The cooling tube 30 and the insert 32 define an inner surface 31 and 33, respectively, that together define a cavity for receiving a molded article 2. A coolant channel 38 is defined between a groove formed through the outer surface of the cooling tube 30 and an inner surface of the sleeve 34 which surrounds the cooling tube 30. In operation, a coolant is circulated in the coolant channel to cool the molded article 2 arranged in the molded article carrier 28. The fastener 36 is configured to connect the cooling tube 30 to a carrier plate (not shown) of a take-off device (not shown). The fastener 36 also defines an axial channel 37 therethrough for connecting the cavity of the molded article carrier 28 to a first air pressure regulator (not shown). In operation, the first air pressure regulator (not shown) is controllably operated to provide a suction air flow from the cavity to receive the molded article 2 therein, or the first air pressure regulator (not shown) is controllably operated to provide an air flow into the cavity to eject the molded article 2 therefrom.
With reference to FIG. 2, a typical molded article picker for use in the foregoing treatment device as a molded article picker 50 is shown. The molded article picker 50 includes a base member 52, a seal member 56, and a tubular pin 58. A base portion of the tubular pin 58 is received in a seat 60 defined in the base member 52 such that the remaining portion of the tubular pin 58 extends from a top surface 51 of the base member 52. A first pressure channel 54 is formed through the base member 52 beneath the seat 60. The first pressure channel 54 connects a second pressure channel 61 that extends through the tubular pin 58 to a second air pressure regulator (not shown). In operation, the second air pressure regulator (not shown) is controllably operated to provide a suction air flow from the region surrounding the tubular pin 58 through a top opening 62 of the second pressure channel 61. The seal member 56 has an annular body. An inner surface 63 of seal member 56 fits tightly around the tubular pin 58 to maintain the seal member 56 in a substantially fixed position with a bottom surface 59 thereof in contact with the top surface 51 of the base member 52.
As will be appreciated by those of skill in the art, a small inaccuracy in the angular positioning of the molded article picker 50 into the pick position can lead to difficulty in reliable picking of the molded articles from the molded article carriers of the take-off device. For example, with reference to FIG. 2 it can be seen that with as little as a 2 degree angular misalignment between the molded article picker 50 and the molded article carrier 28, reference angle α between the centerlines of the molded article carrier 28 and the molded article picker 50, that it is not possible to close a gap G along one side of the top surface 9 of the molded article 2 and the sealing surface 57 of the seal member 56 and hence form a completely enclosed volume between the molded article 2, the tubular pin 58, and the seal member 56 that is the required to effect a reliable vacuum assisted transfer of the molded article 2 from the molded article carrier 28 to the molded article picker 50. The molded article 2 in this example is a preform of the type that is blow molded into a bottle.
One of the problems associated with this prior art approach is that the molded article picker 50 may fail to remove the molded article 2 from the molded article carrier 28 and hence the molded article carrier 28 isn't available to fetch the next hot molded article 2 from the mold forcing the machine operator to disable production and to manually remove the untransferred molded article 2 before resuming production.